<style>
    * { font:12px Arial; }
    .container { background:silver; width:150px; height:30px; }
    .float { background:darkgray; float:left; width:80px; }
    .bfc { background:dimgray; overflow:hidden; color:white; }
</style>
<div class="container">
    <div class="float">FLOAT(80)</div>
    <div class="bfc" style="width:151px;">BFC(151)</div>
</div>
<br />
<div class="container" style="padding-top:5px;">
    <div class="float">FLOAT(80)</div>
    <div class="bfc" style="width:151px;">BFC(151)</div>
</div>
<br />
<div class="container" style="border-top:5px solid black;">
    <div class="float">FLOAT(80)</div>
    <div class="bfc" style="width:151px;">BFC(151)</div>
</div>
<br />
<div class="container" style="display:inline-block;">
    <div class="float">FLOAT(80)</div>
    <div class="bfc" style="width:151px;">BFC(151)</div>
</div>